public TripleMap1 <TPrimaryKey, TSecondary, TTertiary, TValueU> MapValue <TValueU>(Func <TValue, TValueU> f) => new TripleMap1 <TPrimaryKey, TSecondary, TTertiary, TValueU>(PrimaryMap.MapValue(t => Tuple.Create(t.Item1, t.Item2, f(t.Item3))), SecondaryMap, TertiaryMap);
public TwinMap1 <TPrimaryKey, TSecondary, TValueU> MapValue <TValueU>(Func <TValue, TValueU> f) => new TwinMap1 <TPrimaryKey, TSecondary, TValueU>(PrimaryMap.MapValue(t => Tuple.Create(t.Item1, f(t.Item2))), SecondaryMap);
